library to provide command-line commands and sub-commands

 Package commander is a fork of a spin off of golang go tool
 infrastructure to provide commands and sub-commands.
 .
 This package is a fork of t he original commander package, with the
 following modifications:
   - flags could be placed anywhere on the command line
   - flags in whole subcommand tree should be non-conflicting
     (i.e. one name - one value type)
   - interface has changed: first flags should be parsed, then command
     dispatched